Typical navigation systems can be essentially categorized into at least two distinct types, dot-on-the-map and route guidance. The dot-on-the-map type navigation systems are based on topology map databases. These topology map databases are relatively commonplace and many navigation systems have been designed to use this type of map database to guide a traveler between an origin and a destination position. Topology map databases typically are limited to providing elementary topological information. In those map databases used in vehicular navigation systems this may include road segment identification, road segment end points and road segment predecessors and successors. Because these map databases have no traffic flow restriction information, such as one way streets, dead end streets, speed limits, maximum vehicle weight, and maximum vehicle height, to name a few, they are limited in usefulness. This is because if the system is asked to plan and guide the traveler along a route it may plan impossible, or certainly inconvenient, routes for the traveler to follow. Typically, dot-on-the-map systems display an electronic map and a symbol, typically a dot, corresponding to the traveler's present position. The traveler will traverse a route with no advice from the system other than a pointer in the line of sight direction of a selected destination position.
Route guidance systems, on the other hand, generate a route plan between a present position and a selected destination position and then guide the traveler in real time via a series of visual and/or aural guidance instructions.
Both the dot-on-the-map and route guidance systems rely on the availability of maps, typically in the form of digital map databases. Most of the United States, Europe, and Japan are already covered by topology map databases containing road network topology and connectivity information. These topology map databases are adequate for dot-on-the-map type navigation systems.
In contrast, route guidance systems require traffic flow restriction information in addition to the road network topology information provided in the topology databases. The map databases required for this enhanced function are typically known as route guidance maps. In addition to the conventional topological information discussed above they will include various traffic flow restriction information, also introduced above. Availability of these route guidance maps is limited and full global coverage may never be available. Also, coverage for the top forty metropolitan areas in the United States is not expected for some time to come. Since route guidance systems are useful only in areas covered by route guidance map databases, the application of these systems is limited to the relatively few locations having corresponding route guidance map databases until wider map coverage is available.
What is needed is an improved route guidance system that enables a traveler to use either a topology map database or a route guidance database to provide improved navigation capabilities for either navigating in a area covered by a route guidance database or a topology map database. This will enable a user to use either type map database as desired, or as available.